Methods and systems for distance measurement are used in many applications. Examples thereof are extremely precise measurements in geodetic applications, but also measurement tasks in the field of construction installation or for industrial process controllers. For these tasks, stationary, movable, or also handheld distance measuring devices are used, which execute an optical distance measurement to a selected target point. For this purpose, a laser beam is usually emitted and received again and analyzed after reflection on the target. Various measurement principles are available for determining the distance in this case, for example, phase measurement or time-of-flight measurement.
In particular in the field of construction installation or construction removal, portable devices to be held in the hand are used, which are applied in relation to a structure to be surveyed and then carry out a distance measurement to a surface. One typical handheld distance measuring device, which is suitable for such applications, is described, for example, in EP 0 738 899 and EP 0 701 702.
Since a target spot which is visible on the surface to be measured is advantageous for most applications, red lasers are usually used as radiation sources for the distance measurement. Precisions down to the millimeter range are thus achievable with great handling comfort using distance meters of the prior art. Using currently available handheld distance measuring devices, measurements can be carried out from one point to another point, to which a visual connection exists. If the target is concealed, horizontal or vertical dimensions can also be ascertained by means of an inclination sensor.
Various solutions using handheld distance measuring devices having laser distance meters are described in the prior art, by means of which distances can be indirectly measured.
Methods in which the distance measuring device can be held freely in the hand are more comfortable for the user: A method for determining a current position of a distance measuring device is disclosed in EP 1 517 117 A1. In this case, a laser scanner of the distance measuring device scans a spatial segment and detects a plurality of previously attached punctiform referencing means therein, on the basis of which a current position of the distance measuring device can be ascertained. On the other hand, the necessity of preparing the measuring environment in a time-consuming manner by distributing the detectable referencing means therein for the measuring method is disadvantageous.
EP 2 669 707 A1 discloses a further method for indirect determination of distances using a handheld distance measuring device, wherein the distances are ascertained by means of a panoramic image recorded by a camera of the distance measuring device. To execute this method, simultaneously to a measurement of the distance to two spatial points, by an image acquisition unit images are recorded of the environment of the spatial points, which are joined together to form a single panoramic image by means of image stitching, for example, so that a number of pixels between the two spatial points can be ascertained from the images linked to one another. An angle can be ascertained from this number of pixels. The desired distance between the two spatial points can be calculated using the law of cosines. A handheld distance measuring device according to EP 2 669 707 A1 contains for this purpose an image acquisition unit having at least one camera and an image analysis unit for joining together the images and for ascertaining the pixel number. However, this method is essentially only applicable to distances between points on the same plane, for example, on the same wall.